Three dimensional (3D) models of geographical areas, such as topographical maps, may be used for many applications. For example, topographical models may be used in flight simulators. Furthermore, topographical models of man-made structures (e.g., cities) may be extremely helpful in applications such as cellular antenna placement, urban planning, disaster preparedness and analysis, and mapping, for example.
Various types and methods for making 3D models are presently being used. One common 3D model is the digital elevation model (DEM). A DEM is a sampled matrix representation of a geographical area which may be generated in an automated fashion by a computer. In a DEM, coordinate points are made to correspond with a height value.
In order to form DEMs and other topographical models, 3D geospatial data of a target area is first captured. This 3D geospatial data is often combined with 2D image data of that same target data to form a topographical model containing both elevation data as well as intensity data, with the intensity data representing what the target area “looks” like when viewed as highlighted by background radiation, such as visible light from the sun.
Typically, the 3D geospatial data is taken using an active imaging system such as Light Detection and Ranging (LIDAR), and the 2D image data is taken at a later point in time using a passive imaging system such as an image sensor made from conventional photodiodes. To combine the 3D geospatial data with the 2D image data, image registration techniques are used.
An example of such an imagine system is described in U.S. Pat. No. 6,882,409 to Evans et al. Evans et al. discloses a multi-spectral detector for use in a passive/active system. The multi-spectral detection system comprises an optically dispersive element, a detector array, and an integrated circuit. The optically dispersive element is capable of separating received LADAR radiation, and ambient radiation received from a scene into a plurality of spectral components and distributing the separated spectral components. The system also includes a detector array. The detector array includes a plurality of detectors capable of detecting the LADAR radiation, and a plurality of detectors capable of detecting the spectral components of the scene radiation. The integrated circuit is capable of generating a plurality of electrical signals representative of predetermined characteristics of the detected LADAR radiation and the detected spectral components. Thus, this system captures 3D geospatial data using one sensor, captures 2D intensity data with another sensor, and then combines the data, similarly as described above.
Systems such as the Evans et al. system described above, however, often use image registration techniques to combine the 3D and 2D data. These image registration techniques may be costly in terms of computing power, and may not produce desirable results in some situations. As such, further development of geospatial and image collection systems are desired.